1. Field of the Invention
The present invention relates to a film forming unit for a substrate.
2. Description of the Related Art
In the photolithography process in semiconductor device fabrication, for example, resist coating treatment for applying a resist solution to the top surface of a wafer to form a resist film, exposure processing for exposing a pattern on the wafer, developing processing for developing the exposed wafer, and the like are performed to form a predetermined circuit pattern on the wafer.
At present, a spin coating method is in the mainstream as a method of applying a resist solution in the above-described resist coating treatment. According to the spin coating method, the resist solution is discharged to the center of the wafer and the wafer is rotated. This allows the resist solution applied on the wafer to spread by centrifugal force, whereby a uniform resist film can be formed over the entire face of the wafer.
However, in the spin coating method, the wafer is rotated at high speed, whereby a large amount of resist solution scatters from the peripheral portion of the wafer, which results in a big waste of resist solution. Moreover, the unit is contaminated by the scatter of the resist solution, thereby causing adverse effects such as necessity for frequent cleaning.
Therefore, instead of the spin coating method in which the wafer is rotated, a method, in which a nozzle for discharging the resist solution and the wafer are moved relatively to each other to apply the resist solution having low viscosity evenly on the wafer, for example, in a lattice form, is conceivable.
However, also in such a method of applying the resist solution in the manner of a so-called single stroke, there is a fear that a resist film is not uniformly formed since the resist solution applied at the peripheral portion of the wafer swelled by surface tension. Even if exposure is performed with the resist film swelled at the peripheral portion, the swelled peripheral portion becomes a defective portion that can not be used as a product, thereby decreasing yield correspondingly.
The present invention is made in view of the aforesaid points, and its object is to provide a film forming unit for a substrate which forms various kinds of coating films including a resist film having predetermined thickness even at a perimeter portion of the substrate.
In order to attain the above object, according to a first aspect of the present invention, the invention is a film forming unit for applying a coating solution to a substrate and forming a coating film on the substrate, having a heating and/or cooling member brought into direct or indirect contact with the aforesaid substrate for changing temperature of at least a peripheral portion of the aforesaid substrate.
Further, according to a second aspect of the present invention, the invention is a film forming unit for applying a coating solution to a substrate and forming a coating film on the substrate, having a solvent supply device for supplying mist or vapor of a solvent for the aforesaid coating solution to at least a perimeter portion of the aforesaid substrate
By bringing the aforesaid heating and/or cooling member into contact with the substrate and changing the temperature of at least the perimeter portion of the substrate, the temperature of the coating solution applied at least on the perimeter portion of the aforesaid substrate is changed, and thus the surface tension of the coating solution is changed. As a result, at the perimeter portion of the substrate, swelling caused by the surface tension and reduction in film thickness are prevented, whereby a coating film with a predetermined thickness is also formed on the perimeter portion of the substrate. It should be noted that the contact mentioned here is not limited to the expression of the situation in which the substrate and the heating and/or cooling member are joined, but it is also used as a meaning including the situation in which they are close to each other to the extent that the heat of the heating and/or cooling member exerts an influence on the substrate.
Further, by supplying mist or vapor of the solvent to the perimeter portion of the substrate, the tension force of the coating solution applied to the perimeter portion of the substrate can be decreased. Accordingly, on the perimeter portion of the substrate, swelling of the coating solution due to the surface tension can be reduced.
It is preferable that a coating solution discharge portion moving relatively to the aforesaid substrate and discharging the coating solution to the aforesaid substrate is included and that the coating solution discharge portion is made movable relatively to the aforesaid substrate while discharging the coating solution to a top surface of the aforesaid substrate.
It is preferable that the aforesaid heating and/or cooling member has a temperature changing element for controlling the aforesaid heating and/or cooling member at a predetermined temperature. The temperature changing element mentioned here is suitable if it has at least a temperature increasing function when the aforesaid heating and/or cooling member has only a heating function, and it is suitable if it has at least a temperature reducing function when the aforesaid heating and/or cooling member has only a cooling function.
The aforesaid heating and/or cooling member may be provided at a mounting table on which the substrate is placed. The aforesaid heating and/or cooling member may be formed into a ring shape corresponding to a shape of the perimeter portion of the aforesaid substrate, and is allowed to be in contact with an underside surface of the aforesaid substrate. The ring shape mentioned here corresponds to the shape of the perimeter portion of the substrate. Therefore, if the substrate is a square, the outer shape of the aforesaid heating and/or cooling member is a quadrangle, and if the substrate is circular, the outer shape is circular. The aforesaid heating and/or cooling member may be vertically movable. By making it vertically movable, the timing of changing the temperature of the perimeter portion of the substrate and the temperature of the substrate can be controlled.
If the aforesaid heating and/or cooling member has the aforesaid temperature changing element for each divided region and is structured so that a temperature for each region is controllable, different temperatures are set for the respective regions and the temperatures can be controlled. Accordingly, it can be applied to the situation in which the degree of change in the coating solution occurring at the perimeter portion of the substrate differs according to the areas.
Further, it is possible to provide a cooling member for reducing the temperature of the aforesaid substrate inside the aforesaid heating and/or cooling member, and it is also possible to further provide a heating member for heating the aforesaid substrate inside the aforesaid cooling member.